This proposal aims at (1) developing mathematical models to study the genetic differentiation of populations with respect to continuous and quasi-continuous genetic traits both at within- and between-population levels, (2) studying the joint roles of mutation, selection, and/or random genetic drift on such characters, (3) compiling empirical data on genetically determined quantitative characters and physical/physiological abnormalities between different racial groups of man and/or other primates. The ultimate goal is to compare the rate of evolution of such characters with the same at molecular level. It is hoped that the understanding of the evolutionary dynamics of these complex characters may reveal the mode of inheritance of some of the physical/physiological abnormalities which are of biomedical importance. The methods to be adopted here are based on discrete allelic effects which take into account the process of gene substitution, the fundamental source of genetic variability, as opposed to the other continuous effect-models that are being studied elsewhere.